To Prepare a Colloidal Solution (Sol) of Starch

A mixture containing two substances which are insoluble with one another such that one substance remains suspended in another substance is known as a colloidal solution. The particles which remain suspended are microscopic, and their size ranges from 1 to 1000 nm. There are four types of colloids e.g.- sol, emulsion, foam, and aerosol. A sol colloid is a type of colloidal solution in which minute solid particles are dispersed in a liquid medium. E.g.- starch in water, protoplasm, gels, blood etc. Colloidal solutions are heterogeneous, they are highly stable, and show properties such as diffusion and sedimentation.

Table of Contents

• Aim 

• Apparatus Required

• Theory 

• Procedure

• Result

Aim 

To prepare a colloidal starch solution (sol).

Apparatus required

• Beakers

• Glass rod

• Filter paper 

• Mortar and pestle 

• Burner 

• Wire-gauze

• Tripod Stand

Theory

1. Lyophilic sol is the colloidal solution, wherein water is used as a dispersion medium. Starch sol is hydrophilic and hence shows strong, attractive forces with water. 

2. Sol formation requires heating. The process of making a colloidal starch solution (sol) water and starch are heated up to 100 degrees Celsius. 

3. These lyophilic colloids are quite stable and remain unaffected due to the presence of any impurity.

Procedure

1. Weigh 500 mg of starch and put it inside a mortar and pestle.

2. To the mortar and pestle, add a few ml of Distilled water.

3. Grind the starch, make a paste, and pour it into a 50ml beaker.

4. All 100 ml of distilled water in 250 ml of the beaker and put it over a tripod stand, and heat the beaker.

5. Let the water boil, and then slowly pour the starch paste into the water, while constantly stirring the mixture.

6. Allow the mixture to heat for 10 mins, and then cool the beaker.

7. Use filter paper and a funnel to filter the contents inside the beaker.

8. Label the filtered content as ‘starch sol’.

Observations 

A white colour colloidal solution is obtained, which has small starch particles suspended. The dispersion medium here is water, and the dispersion phase is starch particles.

Result

A white-coloured colloidal solution of starch is prepared. Since solid particles are suspended in a liquid medium, and the solid particle shows high affinity towards the liquid, the starch colloidal solution prepared is a lyophilic colloidal sol.

Preparation of colloidal solution of starch

Precautions

1. Clean the apparatus before and after use

2. Use proper distilled water and not tap water.

3. Properly grind the starch particles, or else lumps can be formed.

4. Put the burner's flame at the lowest while pouring the starch paste into the boiling water beaker.

5. Constantly stir the ingredients in the beaker.

6. Be careful while filtering the starch sol.

Lab Manual Questions

1. The starch solution is an example of which kind of solution?

Ans: The starch solution is an example of a hydrophilic colloidal solution. It shows a strong affinity between the dispersed phase and the dispersion medium. 

2. What is sol in chemistry?

Ans: Sol colloid is a colloidal solution in which small solid particles are suspended in a liquid component. The size of the suspended solid particles is very small, and they are microscopic. E.g., Starch in water, blood, muddy water, gelatin etc.

3. What are lyophilic colloids?

Ans: Lyo means the solvent, and philic means loving or attracted to. In the presence of appropriate liquids, these colloids show high forces of attraction with them. Following are examples of lyophilic colloids-Gelatin. Gum, starch, rubber, etc.

4. What is starch? 

Ans: Starch is a type of carbohydrate, a polysaccharide made of numerous glucose monomers joined by 1,4 linkages. It is white-coloured, tasteless and is used to prepare various food items.

Viva Questions 

1. What is a hydrophobic colloid?

Ans: These are water-repelling or water-hating colloidal solutions. In this, the particles dispersed in water show weak attractive forces with water. For, e.g.- soil particles in river water or streams. 

2. Give examples of sol in everyday food items.

Ans: Sol is a colloidal solution between a liquid and a solid. Common food items such as gravies in food, custards, jellies, gelatin etc., are all examples of sol seen in our everyday life.

3. What are emulsions? 

Ans: Emulsions are colloidal solutions made from two liquids that are immiscible in each other. Here, one liquid appears as large droplets in the other liquid. E.g., Egg yolk, Butter, etc.

4. Give examples of solid and liquid aerosols.

Ans:  Solid aerosols are solid particles in a gas, e.g., Smoke, dust, exhaust from cars etc. Liquid aerosols are liquid particles in a gas, e.g., Fog, mist, clouds etc.

5. Give examples of lyophobic sol.

Ans: Lyophobic sols include-Ferric hydroxide sol, Aluminium hydroxide sol, Arsenious sulphide sol, etc.

6. What are the functions of emulsifiers?

Ans: Emulsifiers help in mixing two different immiscible ingredients to get mixed up or combine. They are present in various packaged food products such as cheese, margarine, chocolate, cookies etc. These are food additives and should be taken in limited quantities.

7. What are hydrophobic particles?

Ans: Hydrophobic particles are substances with less affinity towards water, e.g.- alkanes, oils, fats, etc. 

8. What is blood made of?

Ans: Blood is a colloidal solution because it contains RBCs, WBCs, and lymphocytes, which are all suspended in plasma and are made from water.

9. What is heparin?

Ans: Heparin is an anticoagulant with a high negative charge density and is produced by basophils and mast cells of the body and prevents clump-formation inside the blood.

10. Sols show which type of effect?

Ans: A sol is quite stable and shows the Tyndall effect.

Practical Based Questions (MCQs)

1. Find the odd man out

1. Sol

2. Emulsions

3. Aerosols

4. Solvent

Ans: Solvent

2. Ice cream is a type of ____

1. Sol

2. Emulsion

3. Aerosol

4. Foam

Ans: Emulsion

3. What prevents the coagulation of blood?

1. RBCs

2. WBCs

3. Heparin

4. Plasma

Ans: Heparin

4. Which of the following are colloidal solutions?

1. Milk, water, alcohol

2. Paints, Cheese

3. Mist, clouds, butter

4. Both C and B

Ans: Both C and B

5. A colloidal solution is prepared by____

1. By mixing oil and water

2. By adding starch in sulphuric acid

3. Mixing alcohol and water

4. By mixing salt and water 

Ans: By mixing oil and water

6. State which of the following are false-

1. The starch solution, a colloid

2. Milk is a colloid solution

3. Foam colloidal solution is liquid in liquid or solid

4. Aerosol, contain liquid or solids present in the gas

Ans: Foam colloidal solution is liquid in liquid or solid

7. Which of the following are not required in starch solution preparation?

1. Burner

2. Iodine solution

3. Distilled water

4. Glass rod

Ans: Iodine solution

8. A sol is____

1. Solution containing substances

2. A type of colloidal solution

3. Contains only liquids

4. Is made of only gases

Ans: A type of colloidal solution

9. When the medium of suspension is air, then such colloidal solutions are____

1. Emulsions

2. Aerosols

3. Sols

4. Aqueous

Ans:  Aerosols

10. A colloidal solution contains_______

1. Dispersed phase and Continuous medium

2. Solute and solvent

3. Salt and water

4. Solution and solute

Ans: Dispersed phase and Continuous medium

Conclusion

From the above experiment, we can conclude that colloidal solutions are made when two immiscible components are mixed. This causes the dispersed phase to be suspended in the continuous phase. There are 4 types of colloidal solutions as- sols, emulsions, aerosols, and foams. Various colloidal solutions are used in our daily meals, such as milk, ice-creams, butter, starch solutions, gelatin etc.